Grapefruit Seed Extract

Laboratory (in vitro) antibacterial activity. Multiple studies show GSE can inhibit a wide range of bacteria in lab tests (disc diffusion, MIC). That’s the main mechanistic rationale for SIBO: reduce bacterial load in the small intestine. MDPI UCL Discovery

Active compounds / possible mechanisms. GSE contains flavonoids, polyphenols and other phytochemicals with antimicrobial properties; some studies attribute activity to those natural compounds. However — important — many commercial GSE products have been found to contain added synthetic preservatives/biocides (e.g., benzethonium chloride) that explain much of the antimicrobial activity in some tested products. This affects both efficacy and safety. UCL Discovery Science-Based Medicine

Clinical plausibility for SIBO. Because SIBO is an overgrowth of bacteria in the small bowel, any agent with meaningful antibacterial activity could theoretically reduce bacterial counts and symptoms. But plausibility from lab data is not the same as proof in people — the small intestine environment, dosing, absorption, and effects on beneficial flora all matter. No strong clinical proof exists for SIBO specifically. MDPI stuffthatworks.health

• Common formulations: liquid tinctures (drops), capsules/tablets. Liquid is frequently used by practitioners because it’s easy to dose/titrate. Elissa Goodman stuffthatworks.health
• Typical dosing reported in practitioner / patient sources: examples you’ll see online:
• Drops: 20–40 drops (often diluted in water) taken 1–3 times daily. (Example: some naturopath blogs recommend 30–40 drops once or twice daily.) Elissa Goodman
• Capsules: manufacturer labels vary widely (common capsule doses are 100–300 mg per capsule; regimens differ). stuffthatworks.health
• Duration used by patients/practitioners: variable — from a few days to several weeks; some protocols cycle herbal antimicrobials for 2–6 weeks depending on response. There’s no validated duration for SIBO with GSE. stuffthatworks.health Elissa Goodman
• Administration tips seen in practice: take on an empty stomach if aiming at small intestine effect (so compound reaches small bowel), space away from probiotics if you’re using both (to avoid killing the probiotic). These are pragmatic tips rather than evidence-based rules. Elissa Goodman

Bottom line on instructions: because formulations and potency vary a lot and no standardized clinical dosing exists, if anyone considers trying GSE they should first consult their prescribing clinician (especially if they take medications).

No high-quality human RCTs showing GSE cures SIBO. I found in vitro and some animal/in vivo studies of antimicrobial activity, but no randomized controlled clinical trials demonstrating efficacy for human SIBO. (Searches of trial registries and literature do not reveal SIBO RCTs using GSE.) ICHGCP stuffthatworks.health

Representative laboratory/experimental studies:

• Antibiotics (MDPI) review / paper — GSE selected in screens for antibacterial activity vs. multiple strains (disk diffusion, MIC). Shows strong in vitro potency against Gram-positive and some Gram-negative organisms. MDPI
• UCL / discovery PDF — review and experiments summarizing GSE antibacterial effects and mechanisms (in vitro). UCL Discovery
• UTMB / Heggers et al. — an early investigation into processed GSE antibacterial effects and tissue toxicity (investigational). Useful historically but not definitive clinical evidence. UTMB Health Research Expert Profiles
• Recent SciDirect paper (example): GSE evaluated with probiotics vs. C. difficile in vitro / in vivo models — again antimicrobial activity but not SIBO clinical trials. ScienceDirect

Clinical trial registry entries: there are trial registrations involving formulations of grapefruit extract for other indications (not SIBO), but nothing that provides a validated SIBO treatment regimen. ICHGCP